Interrupting use of frequency layer convergence scheme

ABSTRACT

The present invention is directed to interrupting use of a frequency layer convergence scheme that favors selection of a cell on a preferred frequency of a joined point-to-multipoint service. Specifically, a mobile terminal that has joined a point-to-multipoint service having a preferred frequency uses a frequency layer convergence scheme for selecting a cell. The frequency layer convergence scheme favors the selection of a cell on the preferred frequency layer. However, use of the frequency layer convergence scheme is interrupted upon an occurrence of a trigger.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofearlier filing date and right of priority to U.S. ProvisionalApplication No. 60/599,590, filed on Aug. 5, 2004, U.S. ProvisionalApplication No. 60/600,244, filed on Aug. 9, 2004, and U.S. ProvisionalApplication No. 60/601,267, filed on Aug. 12, 2004, the contents ofwhich are hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to cell selection in a wirelesscommunication system, and more particularly, to interrupting use of afrequency layer convergence scheme which favors the selection of a cellon a preferred frequency of a joined point-to-multipoint service.

BACKGROUND OF THE INVENTION

Recently, mobile communication systems have developed remarkably, butfor high capacity data communication services, the performance of mobilecommunication systems cannot match that of existing wired communicationsystems. Accordingly, technical developments for IMT-2000, which is acommunication system allowing high capacity data communications, arebeing made and standardization of such technology is being activelypursued among various companies and organizations.

A universal mobile telecommunication system (UMTS) is a third generationmobile communication system that has evolved from a European standardknown as Global System for Mobile communications (GSM). The UMTS aims toprovide improved mobile communication service based on a GSM corenetwork and wideband code division multiple access (W-CDMA) wirelessconnection technology.

In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the UnitedStates, and TTA of Korea formed a Third Generation Partnership Project(3GPP) for creating the detailed specifications of the UMTS technology.

Within the 3GPP, in order to achieve rapid and efficient technicaldevelopment of the UMTS, five technical specification groups (TSG) havebeen created for performing the standardization of the UMTS byconsidering the independent nature of the network elements and theiroperations.

Each TSG develops, approves, and manages the standard specificationwithin a related region. Among these groups, the radio access network(RAN) group (TSG-RAN) develops the standards for the functions,requirements, and interface of the UMTS terrestrial radio access network(UTRAN), which is a new radio access network for supporting W-CDMAaccess technology in the UMTS.

FIG. 1 illustrates an exemplary basic structure of a general UMTSnetwork. As shown in FIG. 1, the UMTS is roughly divided into a mobileterminal (or user equipment: UE) 10, a UTRAN 100, and a core network(CN) 200.

The UTRAN 100 includes one or more radio network sub-systems (RNS) 110,120. Each RNS 110, 120 includes a radio network controller (RNC) 111,and a plurality of base stations or Node-Bs 112, 113 managed by the RNC111. The RNC 111 handles the assigning and managing of radio resources,and operates as an access point with respect to the core network 200.

The Node-Bs 112, 113 receive information sent by the physical layer ofthe terminal through an uplink, and transmit data to the terminalthrough a downlink. The Node-Bs 112, 113, thus, operate as access pointsof the UTRAN 100 for the terminal.

A primary function of the UTRAN 100 is forming and maintaining a radioaccess bearer (RAB) to allow communication between the terminal and thecore network 200. The core network 200 applies end-to-end quality ofservice (QoS) requirements to the RAB, and the RAB supports the QoSrequirements set by the core network 200. As the UTRAN 100 forms andmaintains the RAB, the QoS requirements of end-to-end are satisfied. TheRAB service can be further divided into an Iu bearer service and a radiobearer service. The Iu bearer service supports a reliable transmissionof user data between boundary nodes of the UTRAN 100 and the corenetwork 200.

The core network 200 includes a mobile switching center (MSC) 210 and agateway mobile switching center (GMSC) 220 connected together forsupporting a circuit switched (CS) service, and a serving GPRS supportnode (SGSN) 230 and a gateway GPRS support node 240 connected togetherfor supporting a packet switched (PS) service.

The services provided to a specific terminal are roughly divided intothe circuit switched (CS) services and the packet switched (PS)services. For example, a general voice conversation service is a circuitswitched service, while a Web browsing service via an Internetconnection is classified as a packet switched (PS) service.

For supporting circuit switched services, the RNCs 111 are connected tothe MSC 210 of the core network 200, and the MSC 210 is connected to theGMSC 220 that manages the connection with other networks.

For supporting packet switched services, the RNCs 111 are connected tothe SGSN 230 and the GGSN 240 of the core network 200. The SGSN 230supports the packet communications going toward the RNCs 111, and theGGSN 240 manages the connection with other packet switched networks,such as the Internet.

Various types of interfaces exist between network components to allowthe network components to transmit and receive information to and fromeach other for mutual communication therebetween. An interface betweenthe RNC 111 and the core network 200 is defined as an Iu interface. Inparticular, the Iu interface between the RNCs 111 and the core network200 for packet switched systems is defined as “Iu-PS,” and the Iuinterface between the RNCs 111 and the core network 200 for circuitswitched systems is defined as “Iu-CS.”

FIG. 2 illustrates a structure of a radio interface protocol between theterminal and the UTRAN according to the 3GPP radio access networkstandards.

As shown in FIG. 2, the radio interface protocol has horizontal layerscomprising a physical layer, a data link layer, and a network layer, andhas vertical planes comprising a user plane (U-plane) for transmittinguser data and a control plane (C-plane) for transmitting controlinformation.

The user plane is a region that handles traffic information of the user,such as voice or Internet protocol (IP) packets, while the control planeis a region that handles control information for an interface of anetwork, maintenance and management of a call, and the like.

The protocol layers in FIG. 2 can be divided into a first layer (L1), asecond layer (L2), and a third layer (L3) based on three lower layers ofan open system interconnection (OSI) standard model. Each layer will bedescribed in more detail as follows.

The first layer (L1), namely, the physical layer, provides aninformation transfer service to an upper layer by using various radiotransmission techniques. The physical layer is connected to an upperlayer called a medium access control (MAC) layer, via a transportchannel. The MAC layer and the physical layer send and receive data withone another via the transport channel.

The second layer (L2) includes a MAC layer, a radio link control (RLC)layer, a broadcast/multicast control (BMC) layer, and a packet dataconvergence protocol (PDCP) layer.

The MAC layer provides an allocation service of the MAC parameters forallocation and re-allocation of radio resources. The MAC layer isconnected to an upper layer called the radio link control (RLC) layer,via a logical channel.

Various logical channels are provided according to the kind oftransmitted information. In general, when information of the controlplane is transmitted, a control channel is used. When information of theuser plane is transmitted, a traffic channel is used. A logical channelmay be a common channel or a dedicated channel depending on whether thelogical channel is shared. Logical channels include a dedicated trafficchannel (DTCH), a dedicated control channel (DCCH), a common trafficchannel (CTCH), a common control channel (CCCH), a broadcast controlchannel (BCCH) and a paging control channel (PCCH) or a Shared ChannelControl Channel (SHCCH). The BCCH provides information includinginformation utilized by a terminal to access a system. The PCCH is usedby the UTRAN to access a terminal.

A Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) refersto a method of providing streaming or background services to a pluralityof UEs using a downlink-dedicated MBMS radio bearer that utilizes atleast one of point-to-multipoint and point-to-point radio bearer. OneMBMS service includes one or more sessions and MBMS data is transmittedto the plurality of terminals through the MBMS radio bearer only whilethe session is ongoing.

As the name implies, an MBMS may be carried out in a broadcast mode or amulticast mode. The broadcast mode is for transmitting multimedia datato all UEs within a broadcast area, for example the domain where thebroadcast is available. The multicast mode is for transmittingmultimedia data to a specific UE group within a multicast area, forexample the domain where the multicast service is available.

For purposes of MBMS, additional traffic and control channels exist. Forexample, an MCCH (MBMS point-to-multipoint Control Channel) is used fortransmitting MBMS control information while an MTCH (MBMSpoint-to-multipoint Traffic Channel) is used for transmitting MBMSservice data.

The different logical channels that exist are listed below:

The MAC layer is connected to the physical layer by transport channelsand can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/shsub-layer, and a MAC-hs sub-layer according to the type of transportchannel to be managed.

The MAC-b sub-layer manages a BCH (Broadcast Channel), which is atransport channel handling the broadcasting of system information. TheMAC-d sub-layer manages a dedicated channel (DCH), which is a dedicatedtransport channel for a specific terminal. Accordingly, the MAC-dsub-layer of the UTRAN is located in a serving radio network controller(SRNC) that manages a corresponding terminal, and one MAC-d sub-layeralso exists within each terminal (UE).

The MAC-c/sh sub-layer manages a common transport channel, such as aforward access channel (FACH) or a downlink shared channel (DSCH), whichis shared by a plurality of terminals, or in the uplink the Radio AccessChannel (RACH). In the UTRAN, the MAC-c/sh sub-layer is located in acontrolling radio network controller (CRNC). As the MAC-c/sh sub-layermanages the channel being shared by all terminals within a cell region,a single MAC-c/sh sub-layer exists for each cell region. Also, oneMAC-c/sh sublayer exists in each terminal (UE). Referring to FIG. 3,possible mapping between the logical channels and the transport channelsfrom a UE perspective is shown. Referring to FIG. 4, possible mappingbetween the logical channels and the transport channels from a UTRANperspective is shown.

The RLC layer supports reliable data transmissions, and performs asegmentation and concatenation function on a plurality of RLC servicedata units (RLC SDUs) delivered from an upper layer. When the RLC layerreceives the RLC SDUs from the upper layer, the RLC layer adjusts thesize of each RLC SDU in an appropriate manner upon consideringprocessing capacity, and then creates certain data units with headerinformation added thereto. The created data units are called protocoldata units (PDUs), which are then transferred to the MAC layer via alogical channel. The RLC layer includes a RLC buffer for storing the RLCSDUs and/or the RLC PDUs.

The BMC layer schedules a cell broadcast message (referred to as a ‘CBmessage’, hereinafter) received from the core network, and broadcaststhe CB messages to terminals located in a specific cell(s). The BMClayer of the UTRAN generates a broadcast/multicast control (BMC) messageby adding information, such as a message ID (identification), a serialnumber, and a coding scheme to the CB message received from the upperlayer, and transfers the BMC message to the RLC layer. The BMC messagesare transferred from the RLC layer to the MAC layer through a logicalchannel, i.e., the CTCH (Common Traffic Channel). The CTCH is mapped toa transport channel, i.e., a FACH, which is mapped to a physicalchannel, i.e., a S-CCPCH (Secondary Common Control Physical Channel).

The PDCP (Packet Data Convergence Protocol) layer, as a higher layer ofthe RLC layer, allows the data transmitted through a network protocol,such as an IPv4 or IPv6, to be effectively transmitted on a radiointerface with a relatively small bandwidth. To achieve this, the PDCPlayer reduces unnecessary control information used in a wired network, afunction called header compression.

A radio resource control (RRC) layer is located at a lowermost portionof the L3 layer. The RRC layer is defined only in the control plane, andhandles the control of logical channels, transport channels, andphysical channels with respect to setup, reconfiguration, and release orcancellation of radio bearers (RBs). The radio bearer service refers toa service provided by the second layer (L2) for data transmissionbetween the terminal and the UTRAN. In general, the setup of the radiobearer refers to the process of defining the characteristics of aprotocol layer and a channel required for providing a specific dataservice, as well as respectively setting detailed parameters andoperation methods.

The RLC layer can belong to the user plane or to the control planedepending upon the type of layer connected at the upper layer of the RLClayer. That is, if the RLC layer receives data from the RRC layer, theRLC layer belongs to the control plane. Otherwise, the RLC layer belongsto the user plane.

The different possibilities that exist for the mapping between the radiobearers and the transport channels are not always possible. The UE/UTRANdeduces the possible mapping depending on the UE state and the procedurethat the UE/UTRAN is executing. The different states and modes areexplained in more detail below.

The different transport channels are mapped onto different physicalchannels. For example, the RACH transport channel is mapped on a givenPRACH, the DCH can be mapped on the DPCH, the FACH and the PCH can bemapped on the S-CCPCH, the DSCH is mapped on the PDSCH and so on. Theconfiguration of the physical channels is given by an RRC signalingexchange between the RNC and the UE.

The RRC mode refers to whether there exists a logical connection betweenthe RRC of the terminal and the RRC of the UTRAN. If there is aconnection, the terminal is said to be in RRC connected mode. If thereis no connection, the terminal is said to be in idle mode. Because anRRC connection exists for terminals in RRC connected mode, the UTRAN candetermine the existence of a particular terminal within the unit ofcells, for example which cell or set of cells the RRC connected modeterminal is in, and which physical channel the UE is listening to. Thus,the terminal can be effectively controlled.

In contrast, the UTRAN cannot determine the existence of a terminal inidle mode. The existence of idle mode terminals can only be determinedby the core network. Specifically, the core network can only detect theexistence of idle mode terminals within a region that is larger than acell, such as a location or a routing area. Therefore, the existence ofidle mode terminals is determined within large regions. In order toreceive mobile communication services such as voice or data, the idlemode terminal must move or change into the RRC connected mode. Thepossible transitions between modes and states are shown in FIG. 5.

A UE in RRC connected mode can be in different states, such as aCELL_FACH state, a CELL_PCH state, a CELL_DCH state or a URA_PCH state.Depending on the states, the UE listens to different channels. Forexample a UE in CELL_DCH state will try to listen (amongst others) toDCH type of transport channels, which comprises DTCH and DCCH transportchannels, and which can be mapped to a certain DPCH. The UE in CELL_FACHstate will listen to several FACH transport channels which are mapped toa certain S-CCPCH physical channel. The UE in PCH state will listen tothe PICH channel and to the PCH channel, which is mapped to a certainS-CCPCH physical channel.

The UE also carries out different actions depending on the state. Forexample, based on different conditions, a UE in CELL_FACH will start aCELL Update procedure each time the UE changes from the coverage of onecell into the coverage of another cell. The UE starts the CELL Updateprocedure by sending to the NodeB a Cell Update message to indicate thatthe UE has changed its location. The UE will then start listening to theFACH. This procedure is additionally used when the UE comes from anyother state to CELL_FACH state and the UE has no C-RNTI available, suchas when the UE comes from the CELL_PCH state or CELL_DCH state, or whenthe UE in CELL_FACH state was out of coverage.

In the CELL_DCH state, the UE is granted dedicated radio resources, andmay additionally use shared radio resources. This allows the UE to havea high data rate and efficient data exchange. However, the radioresources are limited. It is the responsibility of the UTRAN to allocatethe radio resources amongst the UEs such that they are efficiently usedand ensure that the different UEs obtain the quality of servicerequired.

A UE in CELL_FACH state has no dedicated radio resources attributed, andcan only communicate with the UTRAN via shared channels. Thus, the UEconsumes few radio resources. However, the data rate available is verylimited. Also, the UE needs to permanently monitor the shared channels.Thus, UE battery consumption is increased in the case where the UE isnot transmitting.

A UE in CELL_PCH/URA_PCH state only monitors the paging channel atdedicated occasions, and therefore minimizes the battery consumption.However, if the network wishes to access the UE, it must first indicatethis desire on the paging occasion. The network may then access the UE,but only if the UE has replied to the paging. Furthermore, the UE canonly access the network after performing a Cell Update procedure whichintroduces additional delays when the UE wants to send data to theUTRAN.

Main system information is sent on the BCCH logical channel, which ismapped on the P-CCPCH (Primary Common Control Physical Channel).Specific system information blocks can be sent on the FACH channel. Whenthe system information is sent on the FACH, the UE receives theconfiguration of the FACH either on the BCCH that is received on theP-CCPCH or on a dedicated channel. The P-CCPCH is sent using the samescrambling code as a P-CPICH (Primary Common Pilot Channel), which isthe primary scrambling code of the cell. Each channel uses a spreadingcode as commonly done in WCDMA (Wideband Code Division Multiple Access)systems. Each code is characterized by its spreading factor (SF), whichcorresponds to the length of the code. For a given spreading factor, thenumber of orthogonal codes is equal to the length of the code. For eachspreading factor, the given set of orthogonal codes, as specified in theUMTS system, are numbered from 0 to SF-1. Each code can thus beidentified by giving its length (i.e. spreading factor) and the numberof the code. The spreading code that is used by the P-CCPCH is always ofa fixed spreading factor 256 and the number is the number 1. The UEknows about the primary scrambling code either by information sent fromthe network on system information of neighboring cells that the UE hasread, by messages that the UE has received on the DCCH channel, or bysearching for the P-CPICH, which is sent using the fixed SF 256 and thespreading code number 0, and which transmits a fixed pattern.

The system information comprises information on neighboring cells,configuration of the RACH and FACH transport channels, and theconfiguration of MCCH, which is a channel dedicated for MBMS service.When the UE has selected a cell (in CELL_FACH, CELL_PCH or URA_PCHstate), the UE verifies that it has valid system information.

The system information is organized in SIBs (system information blocks),a MIB (Master information block) and scheduling blocks. The MIB is sentvery frequently and provides timing information of the scheduling blocksand the different SIBs. For SIBs that are linked to a value tag, the MIBalso contains information on the last version of a part of the SIBs.SIBs that are not linked to a value tag are linked to an expirationtimer. The SIBs linked to an expiration timer become invalid and need tobe reread if the time of the last reading of the SIB is larger than anexpiration timer value. The SIBs linked to a value tag are only valid ifthey have the same value tag as a value tag broadcast in the MIB. Eachblock has an area scope of validity, such as a Cell, a PLMN (Public LandMobile Network) or an equivalent PLMN, which signifies on which cellsthe SIB is valid. A SIB with the area scope “Cell” is valid only for thecell in which it has been read. A SIB with the area scope “PLMN” isvalid in the whole PLMN. A SIB with the area scope “equivalent PLMN” isvalid in the whole PLMN and equivalent PLMN.

According to the 3GPP standard, a UE in CELL_PCH, URA_PCH or CELL_FACHstate, or in idle mode shall constantly try to select/reselect asuitable cell (for non-emergency calls) or acceptable cell (foremergency calls). In idle mode, when the UE has selected a cell, the UEis commonly referred to as “camping” on the cell. In RRC connected mode,when the UE is in CELL_PCH, URA_PCH, or CELL_FACH state, the UE issimply referred to as having “selected” a cell.

To facilitate the cell reselection, the network transmits in the systeminformation lists of neighboring cells. The lists of neighboring cellsidentify available cells the UE should measure and compare to the cellthe UE has currently selected or the cell the UE camps on. The availablecells may be on the same frequency, on other frequencies or on otherRadio Access Technologies (RATs) such as GSM. The list of cells, andevtl. cells that the UE discovers itself are used as candidates for thecell reselection.

One part of the cell selection/reselection process is based onmeasurements of the quality of the different cells that are part of theneighboring cell list that are candidates for cell reselection. A cellmay or may not be part of a hierarchical cell structure (HCS). This isdefined in the system information of the given cell. In case of thehierarchical cell structure, each cell has a given priority. Dependingon whether the cell is part of the hierarchical cell structure or not,the cell selection procedure changes.

To decide which of the candidate cells to reselect, the UE measures thequality of the neighboring cells. The UE uses a given formula toestablish a ranking criteria R of all candidate cells. The formula isbased on measurements on the CPICH/P-CCPCH and on information receivedin the system information of the candidate cell. The criterion Rcorresponds to a positive or negative value. The R value may becalculated by the following, wherein R_(S) is the R value for theserving cell R_(N) is the R value for neighboring cells:

R_(s) = Q_(meas),_(s)+Qhyst_(s) + QoffmbmsR_(n) = Q_(meas),_(n)−Qoffset_(s, n) + Qoffmbms − TO_(n) * (1 − L_(n))TO_(n) = TEMP_OFFSET_(n) * W(PENALTY_TIME_(n) − T_(n)) $\begin{matrix}{L_{n} = 0} & {\; {{{if}\mspace{14mu} {HCS\_ PRIO}_{n}} = {HCS\_ PRIO}_{s}}} \\{L_{n} = 1} & {\; {{if}\mspace{14mu} {{HCS\_ PRIO}_{n}<>{HCS\_ PRIO}_{s}}}} \\{{W(x)} = 0} & {{{for}\mspace{14mu} x} < 0} \\{{W(x)} = 1} & {{{for}\mspace{14mu} x}>=0}\end{matrix}$

The signaled value Qoffmbms is only applied to those cells (serving orneighboring) belonging to an MBMS Preferred Frequency (i.e., where afrequency convergence scheme is applied). Qmeas gives the quality valueof the received signal derived from the averaged CPICH Ec/No or CPICHRSCP for FDD cells, from the averaged P-CCPCH RSCP for TDD cells andfrom the averaged received signal level for GSM cells. For FDD cells,the measurement that is used to derive the quality value is indicated inSystem Information.

The parameters Qhyst, Qoffsets,n, Qoffmbms, TEMP_OFFSET and PENALTY_TIMEare signaled on System information. The timer T is started and stoppedfor each cell depending on the radio quality of the cell.

If a hierarchical cell structure (HCS) is used, then a criteria H isdefined. The H criterion is a positive or negative value and iscalculated based on information sent in the system information and onmeasurements from the CPICH/P-CPCCH of the candidate cell. In thehierarchical cell structure, a cell may have a different priority. The Hcriterion is calculated according to the following formula:

H_(s) = Q_(meas),_(s)−Qhcs_(s)H_(n) = Q_(meas),_(n)−Qhcs_(n) − TO_(n) * L_(n)

TO_(n) and LN, Q_(meas,s) and Q_(meas,n) are defined similarly to theabove definition. The aim of such a cell structure is to cover in thesame area users that have a low mobility as well as users with a highmobility. To optimize capacity, small-sized cells are preferred toaccommodate as many cells as possible. Accordingly, this enables havinga maximum number of users in a given area.

However, for users that move quickly, it is preferable to havelarge-sized cells to reduce the number of cell changes as the UE moves.To distinguish between large-sized and small-sized cells, differentpriorities are attributed to the cell. The UE tends to select cells withthe highest priority. This generally corresponds to small-sized cells,except when the UE is moving quickly. The H criterion is used in the3GPP standard to take into account the priority. However, when the UEdetects that it is moving quickly (i.e. by detecting that the UEreselects cells often), the UE ceases using the H criteria and no longertakes into account the priority level of the cell. The UE is then saidto be in a “high mobility state”.

A selection criterion S checks whether the received quality of thecandidate cell is sufficient. To do so the, UE measures Q_(qualmeas),which expresses the E_(c)/N₀ of the CPICH of the candidate cell (onlyfor FDD cells). The UE also measures Q_(rxlevmeas), which evaluates theRSCP (Received Signal Code Power) of the CPICH of the candidate cell forFDD cells and the P-CCPCH of the candidate cell for TDD cells. The UEuses these values in an algorithm, together with information received inthe system information of the candidate cell, to calculate the S value.If the S value is higher than 0, the selection criterion S of the cellis fulfilled. Otherwise, it is not fulfilled.

Apart from the criteria R, H and S explained above, other criteria mightdetermine which cell the UE can select. The information on thesecriteria is given to the UE as “cell access restrictions”, which arebroadcast in the system information.

One type of cell access restriction may be “barred cells.” Each UE usesa parameter called “Access Class”, which gives a kind of priority to theUE. The access classes that exist are in the range of 0 to 15. For eachof the access classes in the system information, it can be indicatedwhether a cell is barred or not. A cell can also be barred in general.

Another type of cell access restriction is when a cell is “reserved foroperator use”. In the system information, it can be indicated whether acell is reserved for operator use or not. Depending on whether the UEclass is an operator class or not, and whether the UE is in an emergencycall or not, the UE can reselect a cell which is reserved for operatoruse or not.

Moreover, access to the cell may be restricted because it is “reservedfor future extension”. In the system information, it can be indicatedwhether a cell is reserved for future extension or not.

Access to the cell may be restricted due to a PLMN. Each cell belongs toone or several PLMNs. When a UE is powered on, it selects a PLMN and canonly change the selected PLMN by specific signaling. When the UEselects/reselects a cell, it checks whether the selected PLMNcorresponds to the PLMN of the cell. A UE can use a list of “equivalentPLMNs”, wherein an “equivalent PLMN” is treated as if it was equal tothe selected PLMN. A UE that is not trying to do an emergency call canonly select/reselect cells that belong to the selected PLMN or anequivalent PLMN of the selected PLMN.

An “intra-frequency cell re-selection indicator” is also sent in thesystem information to disallow the UE when the cell the UE has selectedis barred from reselecting another cell on the same frequency.

Accordingly, the above “cell access restriction” attributes limit thenumber of candidate cells the UE can consider for cellselection/reselection. Referring to FIG. 6, a decision process for cellreselection is illustrated.

A major task of the RNC is radio resource management (RRM). DifferentRRC states, transport channels and physical channels with multipleparameters are available in the UMTS standard to optimize use ofavailable radio resources.

A basic method for RRM purposes is the RRC state transition betweenCELL_FACH, CELL_DCH, CELL_PCH and URA_PCH states. Combined with thesestates, when different frequencies are available for communication, theRNC can generally control the number of UEs using a given frequency.However, as described above, in CELL_FACH state, CELL_PCH state andURA_PCH state, the UEs can initiate, based on the measurements and thedifferent rules, the transition from a cell in a given frequency to acell in another frequency. The transition is either based on normalmeasurement and cell selection/reselection rules or based on a frequencylayer convergence scheme.

When the UE is moved from the CELL_DCH state to another state, the UEselects a cell to camp on or connect to. In general, the UE considerscells on all frequencies, except if the RNC indicates a preferredfrequency in an information element (IE) “Frequency Info”. In such acase, the UE preferably selects a cell on the preferred frequency if asuitable cell on the preferred frequency exists.

When the UE is in CELL_FACH state, the RNC may prompt the UE to select acell on another frequency as the preferred frequency by sending amessage including the IE “Frequency Info” to the UE. The UE will thentry to select a cell on the preferred frequency.

The 3GPP system can provide multimedia broadcast multicast service(MBMS). The 3GPP TSG SA (Service and System Aspect) defines variousnetwork elements and their functions required for supporting MBMSservices. A cell broadcast service provided by the prior art is limitedto a service in which text type short messages are broadcast to acertain area. The MBMS service, however, is a more advanced service thatmulticasts multimedia data to terminals (UEs) that have subscribed tothe corresponding service in addition to broadcasting multimedia data.

The MBMS service is a downward-dedicated service that provides astreaming or background service to a plurality of terminals by using acommon or dedicated downward channel. The MBMS service is divided into abroadcast mode and a multicast mode. The MBMS broadcast mode facilitatestransmitting multimedia data to every user located in a broadcast area,whereas the MBMS multicast mode facilitates transmitting multimedia datato a specific user group located in a multicast area. The broadcast areasignifies a broadcast service available area and the multicast areasignifies a multicast service available area.

FIG. 7 illustrates a process of providing a particular MBMS service, byusing the multicast mode. The procedure can be split into two types ofactions, those that are transparent and those that are not transparentto the UTRAN.

The transparent actions are described in the following. A user desiringto receive the MBMS service, first needs to subscribe in order to beallowed to receive MBMS services, to receive information on MBMSservices, and to join a certain set of MBMS services. A serviceannouncement provides the terminal with a list of services to beprovided and other related information. The user can then join theseservices. By joining, the user indicates that the user wants to receiveinformation linked to services that the user has subscribed to andbecomes part of a multicast service group. When a user is no longerinterested in a given MBMS service, the user leaves the service, i.e.,the user is no longer part of the multicast service group. These actionscan be taken by using any means of communication, i.e., the actions maybe done using SMS (Short Messaging Service), or by Internet access.These actions do not have to necessarily be done using the UMTS system.

In order to receive a service for which the user is in a multicast groupthe following actions that are not transparent to the UTRAN areexecuted. The SGSN informs the RNC about a session start. Then the RNCnotifies the UEs of the multicast group that a given service has startedin order to initiate reception of the given service. After havingbroadcast the necessary UE actions and eventually the configuration ofthe PtM bearers for the given service the transmission of the datastarts. When the session stops, the SGSN indicates the stopped sessionto the RNC. The RNC in turn initiates a session stop. The transmissionof the service from the SGSN means for the RNC to provide a bearerservice for conveying the data of the MBMS service.

After the notification procedure, other procedures can be initiatedbetween the UE and the RNC and the SGSN to enable data transmission,such as RRC connection establishment, connection establishment towardsthe PS domain, frequency layer convergence, and counting.

Reception of an MBMS service may be performed in parallel to thereception of other services, such as a voice or video call on the CSdomain, SMS transfer on the CS or PS domain, data transfer on the PSdomain, or any signaling related to the UTRAN or PS or CS domain.

Contrary to the multicast service, for broadcast services, as shown inFIG. 8, only the announcement of the service must be done in atransparent manner. No subscription or joining is needed. Afterwards,the actions that are transparent to the RNC are the same as formulticast services.

Referring to FIG. 9, a typical session sequence from a UTRAN perspectiveis illustrated. As shown, the SGSN informs the RNC about a session start(step 1). The RNC may then perform a counting procedure, which triggerssome UEs to establish a connection to the PS domain (step 2).Consequently, the establishment of an RRC connection for the UEs isinitiated. This allows the RNC to estimate the number of UEs in a givencell that are interested in the service. When the UE has established thePS connection, the SGSN initiates the Iu linking procedure, whichprovides the list of multicast services the UE has joined to the RNC.

For UEs that have an RRC connection established, and which areinterested in the given MBMS service but are not connected to the PSdomain, the RNC sends a specific message to the UEs triggering them toestablish a PS connection (step 3). When the UE has established the PSconnection, the SGSN initiates the Iu linking procedure, which providesthe list of multicast services the UE has joined to the RNC. For UEsthat are not in a CELL_DCH state, a frequency layer convergence schemeallows the RNC to trigger the UEs to change the frequency to which theylisten (step 4).

Depending on the Radio Resource Management (RRM) scheme, the RNCestablishes point-to-multipoint (PtM) or point-to-point (PtP) radiobearers for delivering the MBMS service (step 5 a or 5 b). The RNCdelivers data received from the SGSN to the UEs that are part of themulticast group. After the transmission of the data, the SGSN informsthe RNC about the end of the sessions (step 6). The RNC then releasesthe PtP or PtM radio bearers used for transmitting the MBMS data (step 7a or 7 b).

Generally, for UEs in an RRC connected state, two possibilities exist.The UE will either have a connection established with the PS domain (PMMconnected) or the UE will have no connection established with the PSdomain (PMM idle mode). When there is no connection established with thePS domain, the UE will normally have a connection with the CS domain.Otherwise, the UE is not in an RRC connected mode.

For MBMS, two additional control channels are introduced. They are theMCCH and the MICH (MBMS Notification Indicator Channel). As explainedabove, the MCCH is mapped on the FACH. The MICH is a new physicalchannel and is used to notify users to read the MCCH channel. The MICHis designed to allow the UEs to perform a DRX (Discontinuous Reception)scheme. DRX allows the reduction of battery consumption for UEs whileallowing the UEs to still be aware of any service for which a session isstarting. The MICH may be used to inform the UE of a change in afrequency convergence scheme, change of a configuration of apoint-to-multipoint (PtM) bearer, switch between the PtM bearer and apoint-to-point (PtP) bearer, etc., which all require the MCCH to beread.

The MCCH channel periodically transmits information regarding activeservices, MTCH configuration, frequency convergence, etc. The UE readsthe MCCH information to receive the subscribed services based ondifferent triggers. For example, the UE may be triggered after cellselection/reselection, when the UE is notified of a given service on theMICH, or when the UE is notified via the DCCH channel. The configurationof the MCCH channel is broadcast in the system information. The MICHconfiguration (i.e. spreading code, scrambling code, spreading factorand other information) is either fixed in the standard, or given in thesystem information.

The UMTS standard allows use of different frequency bands for datatransmission. A frequency band in UMTS is in general specified by aUARFCN (UTRA Absolute Radio Frequency Channel Number), which defines thefrequency band used. A given PLMN can use different frequencies.

When a network uses different frequencies, the UEs in a given areaselect one of the frequencies based on the quality measured on thefrequency. The UEs may also select the frequency based on otherparameters given in the system information as explained above. Tobalance the load carried by the different frequencies, the UEs aredistributed among the different frequencies. If a given MBMS service isthen transmitted on a PtM radio bearer to reach UEs in all frequencies,the transmission must be done in all frequencies.

To increase efficiency, it is advantageous to transmit data on onefrequency only and have all UEs interested in a given service reselect acell in that frequency. Accordingly, this functionality is called“frequency convergence”. The frequency layer to which the UEs shouldreselect is called a PFL (Preferred Frequency Layer). As shown in FIG.9, a typical MBMS session contains a period of “frequency convergence”(step 4).

When the frequency convergence process is used for a given service,information regarding the preferred frequency for each service istransmitted in messages either on the MCCH or the system information. Totrigger the reselection to the other frequency, different possibilitiesexist. One possibility is to force the UE to select a cell on thepreferred frequency and to forbid all cells on other frequencies fromparticipating in cell reselection/cell selection.

Another possibility is to change the requirements for cell reselection.This may be done by adding an offset to the R criteria, S criteria or Hcriteria in one of the formulas needed to determine whether cellselection should be done. The offset may be added for the cells on thepreferred frequency or for all cells on the non-preferred frequencies.Other possibilities can be envisaged for having the UE reselect apreferred frequency.

For the hierarchical cell structure, the UE preferably reselects thecell with the highest priority. If a frequency convergence scheme isused, it is implied that the UE must be allowed to select a cell on thepreferred frequency, disregarding the priority of the preferredfrequency. Accordingly, use of the frequency convergence scheme mayimply that the hierarchical cell structure should no longer be used.

A PRACH channel is an uplink channel shared amongst different UEs. Whena UE wants to send data in the uplink on a PRACH channel, a specialmechanism exists to avoid having different UEs transmit at the sametime. This mechanism is called “collision avoidance,” and is implementedin the UMTS system based on a slotted Aloha system. The transmission ofa message on the PRACH channel is described in FIG. 10.

Before transmitting on the PRACH channel, the UE transmits a preamble tothe NodeB. The preamble comprises a code (signature) the UE choosesrandomly amongst the available signatures and transmits it on a specialphysical channel called a RACH sub-channel. The UE repeats thistransmission several times until it receives a positive or negativeacknowledgement indicator or a given number of retransmissions areexceeded. The NodeB listens to all sub-channels and tries to detect thegiven signatures transmitted by the UEs wanting to access the channel.When the NodeB has received the signature, it acknowledges the receptionon a special physical channel (AICH) by transmitting a code forindicating to the UE whether the UE is granted access to the PRACHchannel or not. Accordingly, the simultaneous transmission of severalUEs on the PRACH channel is avoided.

When a UE receives a Not Acknowledged message (NACK) or when the UE doesnot receive any Acknowledged message (ACK) or NACK on the AICH channel,the UE determines whether it is allowed to restart the collisionavoidance process. If another collision avoidance process is allowedaccording to a fixed algorithm, the UE determines the time to waitbefore the next collision avoidance process is started. When the UEreceives the ACK after a collision avoidance process, i.e. when the UEis granted access to the PRACH, the UE transmits a block set on thePRACH channel.

As described above, a frequency convergence scheme optimizes the use ofradio resources by concentrating all UEs interested in a given serviceonto a given frequency. As a result, some UEs may select a cell on apreferred frequency because they are subscribed to a given MBMS serviceeven though the UEs would not select a cell on the preferred frequencyif they were not joined to the MBMS service.

A UE selecting a cell on the “preferred frequency” of an MBMS service toreceive the MBMS service potentially has a worse quality of service.This is because potentially many UEs will select the cell or cells onthe preferred frequency to receive a given MBMS service on the preferredfrequency. Consequently, the load of the cell or cells on the frequencyis increased. Also, the radio quality of the selected cell on thepreferred frequency may be worse than the radio quality of anotherfrequency.

When a UE wants to establish a call or transmit data in the uplink,depending on the state/mode the UE is in, the UE needs to performdifferent actions according to the current standard, as shown in Table1.

TABLE 1 Transmission of Data New Call (C- or U-plane) Idle mode Transmitthe “RRC Transmit the “RRC Connection Request” Connection Request”message on RACH message on RACH channel channel Connected Transmit the“Cell Transmit the “Cell Update” mode/ Update” message on message onRACH channel CELL_PCH RACH channel Connected Transmit the “Cell Transmitthe “Cell Update” mode/ Update” message on message on RACH channelURA_PCH RACH channel Connected Transmit the “Initial Direct Transmit thedata/transmit mode/ Transfer” message on the the “measurement report”CELL_FACH RACH channel message on RACH channel Connected Transmit the“Initial Direct Transmit the data on the mode/ Transfer” message on thededicated transport channel CELL_DCH dedicated transport channel

As described above, a UE using a frequency convergence scheme because itis joined to an MBMS service will potentially have problems transmittingdata on the PRACH channel because of an overloaded cell or bad radioquality. Therefore, a special mechanism is needed to overcome theseproblems.

The frequency convergence mechanism may also conflict with informationon preferred frequencies sent by the RNC at transition from CELL_DCH toCELL_FACH or when the RNC indicates to a UE in a CELL_FACH state toreselect a cell in a given frequency. Accordingly, the efficiency of thesystem is potentially reduced because active UEs cannot be kept on aseparate frequency.

SUMMARY OF THE INVENTION

The present invention is directed to interrupting use of a frequencylayer convergence scheme that favors selection of a cell on a preferredfrequency layer of a joined point-to-multipoint service.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention is embodied in a method for selecting a cell by a mobileterminal in a wireless communication system, the method comprisingjoining a point-to-multipoint service having a preferred frequency,using a frequency layer convergence scheme for selecting the cell,wherein the frequency layer convergence scheme favors the selection ofthe cell on the preferred frequency, and interrupting the use of thefrequency layer convergence scheme upon an occurrence of a trigger.Preferably, the point-to-multipoint service is an MBMS service.

In one aspect of the invention, the trigger for interrupting the use ofthe frequency layer convergence scheme is based on a procedure initiatedwith a network that fails while using the frequency layer convergencescheme. Preferably, the procedure with the network comprisesestablishing a connection with a core network (CN) domain. The CN domainis at least one of a packet switched (PS) domain and a circuit switched(CS) domain.

In another aspect of the invention, the procedure with the networkcomprises at least one of a PRACH access procedure, a radio resourcecontrol (RRC) procedure for transmitting information to the network, amedium access control (MAC) procedure for transmitting data to thenetwork, and a procedure for selecting a cell on a given frequencyaccording to an order received from the network.

In a further aspect of the invention, the trigger for interrupting theuse of the frequency layer convergence scheme comprises receiving amessage for initiating a reconfiguration procedure. Alternatively, thetrigger for interrupting the use of the frequency layer convergencescheme comprises initiating a procedure selecting a cell on a givenfrequency according to an order received from a network.

Preferably, interrupting the use of the frequency layer convergencescheme continues until a timer expires. The timer is started when thefrequency layer convergence scheme is first interrupted, a procedureinitiated with a network comprising a PRACH access procedure fails, aprocedure initiated with a network comprising a medium access control(MAC) procedure for transmitting data to the network fails, or aprocedure initiated with a network comprising a procedure for selectinga cell on a given frequency according to an order received from thenetwork fails.

A value for duration of the timer is received in a system informationmessage from a network. Alternatively, a value for duration of the timeris a fixed value.

Preferably, the method further comprises selecting a cell on a frequencyother than the preferred frequency. Moreover, the method furthercomprises initiating a procedure with a network and continuing tointerrupt the use of the frequency layer convergence scheme until theprocedure initiated with the network ends. Also, the method furthercomprises initiating a procedure with a network, and releasing aconnection with a core network (CN) domain when the procedure initiatedwith the network ends.

In another embodiment of the present invention, a mobile terminal forselecting a cell in a wireless communication system comprises means forjoining a point-to-multipoint service having a preferred frequency,means for using a frequency layer convergence scheme for selecting thecell, wherein the frequency layer convergence scheme favors theselection of the cell on the preferred frequency, and means forinterrupting the use of the frequency layer convergence scheme upon anoccurrence of a trigger. Preferably, the point-to-multipoint service isan MBMS service.

In one aspect of the invention, the trigger for interrupting the use ofthe frequency layer convergence scheme is based on a procedure initiatedwith a network that fails while using the frequency layer convergencescheme. Preferably, the procedure with the network comprisesestablishing a connection with a core network (CN) domain. The CN domainis at least one of a packet switched (PS) domain and a circuit switched(CS) domain.

In another aspect of the invention, the procedure with the networkcomprises at least one of a PRACH access procedure, a radio resourcecontrol (RRC) procedure for transmitting information to the network, amedium access control (MAC) procedure for transmitting data to thenetwork, and a procedure for selecting a cell on a given frequencyaccording to an order received from the network.

In a further aspect of the invention, the trigger for interrupting theuse of the frequency layer convergence scheme comprises receiving amessage initiating a reconfiguration procedure. Alternatively, thetrigger for interrupting the use of the frequency layer convergencescheme comprises initiating a procedure for selecting a cell on a givenfrequency according to an order received from a network.

Preferably, interrupting the use of the frequency layer convergencescheme continues until a timer expires. The timer is started when thefrequency layer convergence scheme is first interrupted, a procedureinitiated with a network comprising a PRACH access procedure fails, aprocedure initiated with a network comprising a medium access control(MAC) procedure for transmitting data to the network fails, or aprocedure initiated with a network comprising a procedure for selectinga cell on a given frequency according to an order received from thenetwork fails.

A value for duration of the timer is received in a system informationmessage from a network. Alternatively, a value for duration of the timeris a fixed value.

Preferably, the mobile terminal further comprises means for selecting acell on a frequency other than the preferred frequency. Moreover, themobile terminal further comprises means for initiating a procedure witha network and means for continuing to interrupt the use of the frequencylayer convergence scheme until the procedure initiated with the networkends. Also, the mobile terminal further comprises means for initiating aprocedure with a network and means for releasing a connection with acore network (CN) domain when the procedure initiated with the networkends.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments.

FIG. 1 is a block diagram of a general UMTS network architecture.

FIG. 2 is a block diagram of a structure of a radio interface protocolbetween a terminal and a network based on 3GPP radio access networkstandards.

FIG. 3 illustrates the mapping of logical channels onto transportchannels in the mobile terminal.

FIG. 4 illustrates the mapping of logical channels onto transportchannels in the network.

FIG. 5 illustrates possible transitions between modes and states in theUMTS network.

FIG. 6 illustrates a decision process for cell selection.

FIG. 7 illustrates a process of providing a particularpoint-to-multipoint service using a multicast mode.

FIG. 8 illustrates a process of providing broadcast services.

FIG. 9 illustrates a session sequence from a network perspective.

FIG. 10 is flow chart for transmitting a message on a PRACH channel.

FIG. 11 illustrates the interruption of a frequency layer convergencescheme in accordance with one embodiment of the present invention.

FIG. 12 illustrates the interruption of a frequency layer convergencescheme using a timer in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a UE having joined a service for whicha “preferred frequency” is defined but should not use a “frequency layerconvergence” scheme under certain circumstances. For example, thefrequency layer convergence scheme should not be used when the UE triesto establish a new call, or when the UE fails to access the network onthe preferred frequency while using a method favoring a preferredfrequency of a joined MBMS service.

Several methods exist for determining whether the UE should stopapplying a method favoring the selection of a cell on a given “preferredfrequency”. Preferably, when the frequency layer convergence scheme isinterrupted for the preferred frequency, it should be interrupted forany service for which the preferred frequency is the given frequency.

In accordance with a first embodiment of the present invention, the UEstops using the frequency layer convergence scheme when certainconditions occur as a result of using the frequency convergence scheme.Preferably, during a PRACH access procedure, when the UE receives in aMAC layer notification that a collision avoidance process has failed ina physical layer, or when the UE receives a NACK on the AICH channel orreceives no response at all from a NodeB, or when a MAC procedure fortransmitting data on the preferred frequency fails as a result of the UEusing the frequency layer convergence scheme, the UE ceases to use thescheme.

In accordance with a second embodiment of the present invention, the UEstops using the frequency layer convergence scheme when the UE mustperform a specific procedure, such as when the UE tries to perform anemergency call. Another specific procedure is when the NAS (Non-AccessStratum) layers indicate to the AS (Access Stratum) layer of the UE toestablish a connection with a CN domain for a specific reason, such asOriginating Conversational Call, Originating Streaming Call, OriginatingInteractive Call, Originating Background Call, Originating SubscribedTraffic Call, Terminating Conversational Call, Terminating StreamingCall, Terminating Interactive Call, Terminating Background Call,Emergency Call, Inter-RAT cell re-selection, Inter-RAT cell changeorder, Registration, Detach, Originating High Priority Signaling,Originating Low Priority Signaling, Call Re-establishment, TerminatingHigh Priority Signaling, Terminating Low Priority Signaling,Terminating-cause unknown, or any subset of these reasons.

In accordance with a third embodiment of the present invention, the UEstops using the frequency layer convergence scheme when the UE is askedto select a cell on a given frequency, either in CELL_FACH state, inCELL_PCH state, in URA_PCH state or in idle mode.

When the UE stops using the frequency layer convergence scheme for oneof the above reasons, it becomes necessary to also define a method forrestarting the frequency layer convergence scheme again. Preferably, atrigger for restarting the frequency layer convergence scheme may bewhen the procedure that triggered the stoppage of the frequency layerconvergence scheme is finished successfully or unsuccessfully.Alternatively, at a point when use of the frequency layer convergencescheme is stopped, the UE may start a timer such T_(freq) _(—) _(conv)_(—) _(int). At the end of a time period of the timer, use of thefrequency layer convergence scheme is restarted. Accordingly, thislimits interruption of the use of the frequency layer convergencescheme. Preferably, the timer is broadcast on the system information ofthe cell.

Referring to FIG. 11, a method for executing an emergency call by a UEwith respect to a frequency layer convergence scheme is illustrated.Initially, the UE in a CELL_FACH, CELL_PCH, URA_PCH or idle mode beginsusing a frequency layer convergence scheme (step 1). This allows the UEto reselect a preferred frequency. Subsequently, when NAS indicates tothe AS that a connection to a CN domain must be established, a specificcause value is given to the UE (step 2).

Based on the cause value, the UE may stop use of the frequency layerconvergence scheme (step 3). Accordingly, when the UE stops using thefrequency layer convergence scheme, the UE changes the way it evaluatesthe neighboring cells. When the UE needs to establish a connection to acore network domain when the UE is in an idle mode, CELL_FACH, CELL_PCHor URA_PCH state, it is implied that the UE must transmit a message,such as Cell Update, RRC Connection Request and/or Initial Directtransfer, on the PRACH channel to the NodeB (step 4).

When the current cell or cells on the current frequency are loaded, thePRACH channel access may fail on the current frequency (step 5).Eventually, the UE will reselect a cell on another frequency as thepreferred frequency since the frequency layer convergence scheme is nolonger used (step 6). After the cell reselection, access to the PRACHwill have a higher chance of succeeding because the best cell is chosen(step 7).

After the call is finished, the connection to the CN domain is released(step 8). The UE will then restart use of the frequency layerconvergence scheme if it is still applied (step 9).

Referring to FIG. 12, a method for stopping frequency layer convergenceby a UE based on a timer is illustrated. Initially, the UE in aCELL_FACH, CELL_PCH, URA_PCH or idle mode begins using a frequency layerconvergence scheme (step 1). This allows the UE to reselect a preferredfrequency.

Subsequently, any one of a number of events may occur (step 2). Forexample, the NAS may indicate to the AS that a connection to a CN domainmust be established and gives a specific cause value to the UE. Or anRRC procedure is started which requires transmission in the uplink.Also, the transmission of data in the uplink may be started. Or the UEmay be ordered to select a cell on a given preferred frequency.

Accordingly, the UE ceases use of the frequency layer convergencescheme. When the UE stops using the frequency layer convergence scheme,the UE will change the way it evaluates the neighboring cells. Also,upon stopping the use of the scheme, the UE starts a timer T_(freq) _(—)_(conv) _(—) _(int) (step 3). The duration of the timer may be a fixedvalue, or the UE may utilize a value read in the system information.

The UE then transmits data on the PRACH channel to the NodeB (step 4).When the current cell or cells on the current frequency are loaded, thePRACH channel access may fail on the current frequency (step 5).

An alternative to starting the timer T_(freq) _(—) _(conv) _(—) _(int)in step 3 is to start it once the first PRACH access procedure hasfailed (step 6). The PRACH access procedure may fail due to a receptionof a NACK, no reception of a response message, or when a retry mechanismin the MAC layer has timed out, such that there is no moreretransmission. The duration of the timer may be a fixed value, or theUE may utilize a value read in the system information.

Eventually, the UE will reselect a cell on another frequency as thepreferred frequency since the method for frequency layer convergencescheme is no longer used (step 7). After the cell reselection, access tothe PRACH will have a higher chance of success because the best cell ischosen (step 8).

When the timer T_(freq) _(—) _(conv) _(—) _(int) expires and after thecall has ended, the connection to the CN domain is released (step 9).The UE will then restart use of the frequency layer convergence schemeif it is still applied (step 10).

Accordingly, the present invention ensures a UE having joined an MBMSservice, will have the same or similar chance of success in establishinga new call/emergency call or transmitting data, as the same UE nothaving joined an MBMS service.

Although the present invention is described in the context of mobilecommunication, the present invention may also be used in any wirelesscommunication systems using mobile devices, such as PDAs and laptopcomputers equipped with wireless communication capabilities. Moreover,the use of certain terms to describe the present invention should notlimit the scope of the present invention to a certain type of wirelesscommunication system. The present invention is also applicable to otherwireless communication systems using different air interfaces and/orphysical layers, for example, TDMA, CDMA, FDMA, WCDMA, etc.

The preferred embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.).

Code in the computer readable medium is accessed and executed by aprocessor. The code in which preferred embodiments are implemented mayfurther be accessible through a transmission media or from a file serverover a network. In such cases, the article of manufacture in which thecode is implemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration without departing from the scope of the presentinvention, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuredescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

1-36. (canceled)
 37. A method of frequency selection for an MBMS(Multimedia Broadcast/Multicast Service) service, the method performedby a mobile terminal and comprising: receiving a message that instructsan interruption of a MBMS frequency selection procedure, wherein themessage initiates a reconfiguration procedure; and stopping the MBMSfrequency selection procedure if the mobile terminal is not in CELL_DCHstate, wherein the MBMS frequency selection procedure allows the mobileterminal to select a preferred frequency of the MBMS service.
 38. Themethod of claim 37, wherein the received message includes a specificvalue that is used to stop the MBMS frequency selection procedure. 39.The method of claim 37, wherein the mobile terminal is not in CELL_DCHstate means that the mobile terminal is in CELL_FACH state, in CELL_PCHstate, in URA_PCH state or in idle mode.
 40. The method of claim 37,wherein the MBMS frequency selection procedure uses a frequency layerconvergence scheme for selecting a cell, wherein the frequency layerconvergence scheme favors the selection of the cell on the preferredfrequency of the MBMS service.
 41. The method of claim 37, wherein theuse of the frequency layer convergence scheme is interrupted uponreceiving the message that initiates the reconfiguration procedure. 42.The method of claim 41, wherein a trigger for interrupting the use ofthe frequency layer convergence scheme is based on a procedure initiatedwith a network that fails while using the frequency layer convergencescheme.
 43. The method of claim 42, wherein the procedure with thenetwork comprises establishing a connection with a core network (CN)domain, wherein the CN domain is at least a packet switched (PS) domainor a circuit switched (CS) domain.
 44. The method of claim 42, whereinthe procedure with the network comprises at least: a PRACH accessprocedure; a radio resource control (RRC) procedure for transmittinginformation to the network; a medium access control (MAC) procedure fortransmitting data to the network; or a procedure for selecting a cell ona given frequency according to an order received from the network. 45.The method of claim 41, wherein a trigger for interrupting the use ofthe frequency layer convergence scheme comprises: initiating a procedurefor selecting a cell on a given frequency according to an order receivedfrom the network.
 46. A mobile terminal that performs frequencyselection for an MBMS (Multimedia Broadcast/Multicast Service) service,the mobile terminal comprising: means for receiving a message thatinstructs an interruption of a MBMS frequency selection procedure,wherein the message initiates a reconfiguration procedure; and means forstopping the MBMS frequency selection procedure if the mobile terminalis not in CELL_DCH state, wherein the MBMS frequency selection procedureallows the mobile terminal to select a preferred frequency of the MBMSservice.
 47. The mobile terminal of claim 46, wherein the receivedmessage includes a specific value that is used to stop the MBMSfrequency selection procedure.
 48. The mobile terminal of claim 46,wherein the mobile terminal is not in CELL_DCH state means that themobile terminal is in CELL_FACH state, in CELL_PCH state, in URA_PCHstate or in idle mode.
 49. The mobile terminal of claim 46, wherein theMBMS frequency selection procedure uses a frequency layer convergencescheme for selecting a cell, wherein the frequency layer convergencescheme favors the selection of the cell on the preferred frequency ofthe MBMS service.
 50. The mobile terminal of claim 49, wherein the useof the frequency layer convergence scheme is interrupted upon receivingthe message that initiates the reconfiguration procedure.
 51. A methodof transmitting a message in order for a mobile terminal to performfrequency selection for an MBMS (Multimedia Broadcast/Multicast Service)service, the method performed by a network and comprising: transmittingthe message that instructs an interruption of a MBMS frequency selectionprocedure, wherein the message initiates a reconfiguration procedure,wherein the mobile terminal stops the MBMS frequency selection procedureaccording to the transmitted message if the mobile terminal is not inCELL_DCH state, and wherein the MBMS frequency selection procedureallows the mobile terminal to select a preferred frequency of the MBMSservice.
 52. The method of claim 51, wherein the transmitted messageincludes a specific value that is used to stop the MBMS frequencyselection procedure.
 53. The method of claim 51, wherein the mobileterminal is not in CELL_DCH state means that the mobile terminal is inCELL_FACH state, in CELL_PCH state, in URA_PCH state or in idle mode.54. The method of claim 51, wherein the MBMS frequency selectionprocedure uses a frequency layer convergence scheme for selecting acell, wherein the frequency layer convergence scheme favors theselection of the cell on the preferred frequency of the MBMS service.55. The method claim 54, wherein the use of the frequency layerconvergence scheme is interrupted according to the message thatinitiates the reconfiguration procedure.